package org.apache.lucene.search;

import org.apache.lucene.index.IndexReader;

import java.io.IOException;

/**
 * Abstract base class for sorting hits returned by a Query.
 *
 * <p>This class should only be used if the other SortField
 * types (SCORE, DOC, STRING, INT, FLOAT) do not provide an
 * adequate sorting.  It maintains an internal cache of values which
 * could be quite large.  The cache is an array of Comparable,
 * one for each document in the index.  There is a distinct
 * Comparable for each unique term in the field - if
 * some documents have the same term in the field, the cache
 * array will have entries which reference the same Comparable.
 *
 * <p>Created: Apr 21, 2004 5:08:38 PM
 *
 * @author  Tim Jones
 * @version $Id: SortComparator.java 150541 2004-09-29 15:09:02Z goller $
 * @since   1.4
 */
public abstract class SortComparator implements SortComparatorSource {

    // inherit javadocs
    public ScoreDocComparator newComparator(final IndexReader reader, final String fieldname) throws IOException {
        final String field = fieldname.intern();
        final Comparable[] cachedValues = FieldCache.DEFAULT.getCustom(reader, field, SortComparator.this);

        return new ScoreDocComparator() {

            public int compare(ScoreDoc i, ScoreDoc j) {
                return cachedValues[i.doc].compareTo(cachedValues[j.doc]);
            }

            public Comparable sortValue(ScoreDoc i) {
                return cachedValues[i.doc];
            }

            public int sortType() {
                return SortField.CUSTOM;
            }
        };
    }

    /**
     * Returns an object which, when sorted according to natural order,
     * will order the Term values in the correct order.
     * <p>For example, if the Terms contained integer values, this method
     * would return <code>new Integer(termtext)</code>.  Note that this
     * might not always be the most efficient implementation - for this
     * particular example, a better implementation might be to make a
     * ScoreDocLookupComparator that uses an internal lookup table of int.
     * @param termtext The textual value of the term.
     * @return An object representing <code>termtext</code> that sorts according to the natural order of <code>termtext</code>.
     * @see Comparable
     * @see ScoreDocComparator
     */
    protected abstract Comparable getComparable(String termtext);

}